From 3bf3dadbc02736c66f56754769dcc001b040862b Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 7 Sep 2023 06:57:08 +0000
Subject: [PATCH] Ensure that dyn trait bounds stay sorted

---
 compiler/rustc_middle/src/ty/print/pretty.rs  | 19 ++++++++-----------
 .../object/enforce-supertrait-projection.rs   |  2 +-
 .../enforce-supertrait-projection.stderr      |  2 +-
 .../dont-suggest-unsize-deref.rs              |  2 +-
 .../dont-suggest-unsize-deref.stderr          |  8 ++++----
 5 files changed, 15 insertions(+), 18 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index ac0c88468fa..83c9269f24e 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1239,21 +1239,18 @@ pub trait PrettyPrinter<'tcx>:
                         .generics_of(principal.def_id)
                         .own_args_no_defaults(cx.tcx(), principal.args);
 
-                    let mut projections = predicates.projection_bounds();
-
-                    let mut args = args.iter().cloned();
-                    let arg0 = args.next();
-                    let projection0 = projections.next();
-                    if arg0.is_some() || projection0.is_some() {
-                        let args = arg0.into_iter().chain(args);
-                        let projections = projection0.into_iter().chain(projections);
+                    let mut projections: Vec<_> = predicates.projection_bounds().collect();
+                    projections.sort_by_cached_key(|proj| {
+                        cx.tcx().item_name(proj.item_def_id()).to_string()
+                    });
 
+                    if !args.is_empty() || !projections.is_empty() {
                         p!(generic_delimiters(|mut cx| {
-                            cx = cx.comma_sep(args)?;
-                            if arg0.is_some() && projection0.is_some() {
+                            cx = cx.comma_sep(args.iter().copied())?;
+                            if !args.is_empty() && !projections.is_empty() {
                                 write!(cx, ", ")?;
                             }
-                            cx.comma_sep(projections)
+                            cx.comma_sep(projections.iter().copied())
                         }));
                     }
                 }
diff --git a/tests/ui/traits/object/enforce-supertrait-projection.rs b/tests/ui/traits/object/enforce-supertrait-projection.rs
index 2c9b41eea2a..0ea944ec2df 100644
--- a/tests/ui/traits/object/enforce-supertrait-projection.rs
+++ b/tests/ui/traits/object/enforce-supertrait-projection.rs
@@ -7,7 +7,7 @@ trait Trait: SuperTrait<A = <Self as SuperTrait>::B> {}
 
 fn transmute<A, B>(x: A) -> B {
     foo::<A, B, dyn Trait<A = A, B = B>>(x)
-    //~^ ERROR type mismatch resolving `<dyn Trait<B = B, A = A> as SuperTrait>::A == B`
+    //~^ ERROR type mismatch resolving `<dyn Trait<A = A, B = B> as SuperTrait>::A == B`
 }
 
 fn foo<A, B, T: ?Sized>(x: T::A) -> B
diff --git a/tests/ui/traits/object/enforce-supertrait-projection.stderr b/tests/ui/traits/object/enforce-supertrait-projection.stderr
index 848b4e69a4b..2fb94d34896 100644
--- a/tests/ui/traits/object/enforce-supertrait-projection.stderr
+++ b/tests/ui/traits/object/enforce-supertrait-projection.stderr
@@ -1,4 +1,4 @@
-error[E0271]: type mismatch resolving `<dyn Trait<B = B, A = A> as SuperTrait>::A == B`
+error[E0271]: type mismatch resolving `<dyn Trait<A = A, B = B> as SuperTrait>::A == B`
   --> $DIR/enforce-supertrait-projection.rs:9:17
    |
 LL | fn transmute<A, B>(x: A) -> B {
diff --git a/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.rs b/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.rs
index 8133036991c..c6f9e345618 100644
--- a/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.rs
+++ b/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.rs
@@ -9,7 +9,7 @@ where
     I: Iterator<Item = i32>,
 {
     use_iterator(i);
-    //~^ ERROR `&dyn IntoIterator<Item = i32, IntoIter = I>` is not an iterator
+    //~^ ERROR `&dyn IntoIterator<IntoIter = I, Item = i32>` is not an iterator
 }
 
 fn main() {}
diff --git a/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.stderr b/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.stderr
index 18ce9939eb2..bd0e7ca2c02 100644
--- a/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.stderr
+++ b/tests/ui/traits/suggest-dereferences/dont-suggest-unsize-deref.stderr
@@ -1,13 +1,13 @@
-error[E0277]: `&dyn IntoIterator<Item = i32, IntoIter = I>` is not an iterator
+error[E0277]: `&dyn IntoIterator<IntoIter = I, Item = i32>` is not an iterator
   --> $DIR/dont-suggest-unsize-deref.rs:11:18
    |
 LL |     use_iterator(i);
-   |     ------------ ^ `&dyn IntoIterator<Item = i32, IntoIter = I>` is not an iterator
+   |     ------------ ^ `&dyn IntoIterator<IntoIter = I, Item = i32>` is not an iterator
    |     |
    |     required by a bound introduced by this call
    |
-   = help: the trait `Iterator` is not implemented for `&dyn IntoIterator<Item = i32, IntoIter = I>`
-   = note: required for `&dyn IntoIterator<Item = i32, IntoIter = I>` to implement `IntoIterator`
+   = help: the trait `Iterator` is not implemented for `&dyn IntoIterator<IntoIter = I, Item = i32>`
+   = note: required for `&dyn IntoIterator<IntoIter = I, Item = i32>` to implement `IntoIterator`
 note: required by a bound in `use_iterator`
   --> $DIR/dont-suggest-unsize-deref.rs:3:8
    |